Lead glass having low power factor



Patented Jan. 2 2, 1946 LEAD GLASS HAVING LOW POWER FACTOR WilliamHouston Armlstead, Jr., Corning, N. Y., asslgnor to Corning Glass Works,Corning, N. Y., a corporation of New York No Drawing. Application July11, 1944, Serial No. 544,466

6 Claims. (01. 106-53) This invention relates to glass compositions andhas for its primary object to provides. new and useful glass havingcertain special characteristics making it particularly suitable as aninsulating medium for use in electrical condensers for radio circuits. Aglass having these characteristics would be a welcome substitute formica which is ordinarily used for this purpose and which is expensiveand requires considerable selection to insure suitable uniformity inquality. Glass,. on the other hand, can be manufactured relativelycheaply and with great uniformity in composition and properties.However, no glass has heretofore been devised which combines the desiredcharacteristics to the-extent that does the glass herein claimed.

The desired characteristics are:

A- power factor less than .07%', as measured at a frequency of onemegacycle at room temperature.

A dielectric constant of at least 4 and preferably '7 on 8.

A temperature coeflicient less than 100 parts per million per degreecentigrade. By temperature coefllclent is meant the rate of change ofthree centimeters long will elongate at the rate of one millimeter perminute when heated throughout the upper nine centimeters of its length.

oxide and lead oxide, compositions may be produced which have low powerfactors and low temperature coefficients and also relatively low Any andall of these properties may easily be r I obtained at the sacrifice ofothers. Many glasses are known which have low power factors but theylack one or more of the above mentioned properties and hence have notbeen entirely suitable for use in the insulation ofcondensers forcircuits carrying radio frequency currents. In such circuits the powerlosses caused by lack of these properties may be quite substantial. Theproblem solved by me has been to obtain all of the desired properties inon glass.

'Pure silica has a very low power factor and also a sufficiently lowtemperature coefficient for the present purpose but, the high fusingpoint of silica and its extremely high viscosity when fused are wellknown and preclude its present use. I have found that, when silica isfluxed with boric 1%.of alumina. v

In general, mynew glasses consist of a homo.-'

softening points. However, such compositions to a large extent separateinto two immiscible phases or compositions on cooling and are so weakstructurally that they crumble.

I have now found that the addition of 5% to 15% of alumina to suchcompositions prevents the formation of separate phases and renders allcomponents miscible. At the same time, the chemical stability of theglasses is improved, the power factor is decreased, the dielectricconstant is increased, and the temperature coefllcient is notsubstantially changed. This result is entirely unexpected, because theintroduction of alumina into an alkali-containing borosilicate raisesthe power factor'by as much as .02% for every geneous mixture of 20% to.40% PhD, 5% to 15% A1202. 5% to %320: and 10% to 50% S102. Thesecompositions have power factors less than .07%, dielectric constantsgreater than 5, temperature coefllcients' less than 100 P. P. M. perdegree 0. and softening points less than 800 C. If desired, thesoftening points and power factors can be lowered somewhat further bythe introduction of fluorine, preferably bythe addition of 5% to 10% oflead fluoride in lieu of lead oxide.

As examples of glasses in accordance with my invention, the followingcompositions, calculated in percent. by weight from their respectivebatches together with their properties are given:

S10 35 30 25 50 10 30 B 0; 20 20 20 20 50 20 PhD 40 40 40 20 30 30 PbF'1O A1 0; 5 .10 15 10 10 10 Power factor percent .069 .065 .063 .050 .057-.060 Dielectric coasts??? 6.85 7.5 7.72 5.4 6.2 7.5

ecoe 90 90 90 Softening temp., C 570 615 658 786 500 600 Expansion00efl.x10 2 47 46. 5 45. 6 34 58 47 The values for power factor weremeasured by shows that power factor decreases and dielectric constantincreases with increase in alumina.

A dielectric constant greater than 5, a tempera- I ture coefllcient lessthan 100 parts per million per C., a softening point less than 800 C.,and consisting of compounds of lead, aluminum, boron and silicon inproportions equivalent to 20% to 40% PhD, 5% to 15% A1203, 5% to 65%B203, and to 50% Si02.

2. A glass having a power factor less than .07%,

a dielectric constant greater than 5, a temperature coemcient less than100 parts per million per CI, a softening point less than 800 C., andconsisting of 20% to 40% P100, 5% to A1203, 5% to 65% B203, and 10% to50% SiOz.

3. A glass having a, power factor less than .07 a dielectric constantgreater than 5, a temperature coefflcient less than 100 parts permillion per C., a softening point less than 800 0., and consisting ofcompounds of lead, aluminum, boron, and silicon in proportionsequivalent to to PhD, 5% to 15% Al2Oa,-5% to 65% B103, and 10% to S102and a small amount of fluorine.

4. A glass having a power factor less than .07%, a dielectric constantgreater than 5, a temperature coefflcient less than 100 parts permillion per C., a. softening point less than 800 0., and consisting of20% to 40% P100, 5% to 15% A1203, 5% to B203, and 10% to 50% S102, andshowing by analysis the presence of fluorine. 5. A glass having a powerfactor less than .07%, a dielectric constant greater. than 5, atempera.- ture coeflicient, less than parts per million per .C., asoftening .point less than 800 C., and consisting of compounds of lead,aluminum, boron and siliconin proportions equivalent to approximately30% SiO2, 20% B203, 40% P100, and 10% A1203.

6. A glass having a power factor less than .07%, a dielectric constantgreater than 5., a. temperature coefficient less than 100 parts permillion per C., a softening point less than 800 0., and consisting ofcompounds of lead, aluminum, boron and silicon in proportions equivalentto approximately 30% SiOz, 20% B203, 30% PbO, 10% PbFz and 10% A1202.

WILLIAM HOUSTON ARMISTEAD, JR.

